Iron tetrahedron

Figure 36 Pictorial representation of the iron tetrahedron with encapsulated BF4 ion and four tetrahedron-face-capping Bp4 ions of the trication [(BF4) C [MeC(CH2PPh2)3Fe"]4(NCC2H2CN)J 0 (BF4)4) + of 86.

The simplest iron-sulfur centers, which were first discovered in ru-bredoxins, consist of one iron ion coordinated by a distorted tetrahedron of cysteinyl sulfur atoms. This environment provides a weak ligand field giving a spin equal to and 2 when the ion is Fe(III) and Fe(II), respectively. It also determines the splitting of the ground spin manifold, and consequently the characteristics of the EPR spectrum. This splitting is generally described in the framework of the spin Hamiltonian ... 

Saha AK, Hossain MM (1993) Synthesis of a polymer-bound iron Lewis acid and its utilization in Diels-Alder reactions. Tetrahedron Lett 34 3833-3836 Olson AS, Seitz WJ, Hossain MM (1991) Transition metal catalysis of the Diels-Alder reaction. Tetrahedron Lett 32 5299-5302... 

Corey EJ, Bhattacharyya S (1977) Total Synthesis of Enterobactin, a Macrocyclic Iron Transporting Agent of Bacteria. Tetrahedron Lett 3919... 

Fukasawa K, Goto M, Sasaki K, Hirata Y, Sato S (1972) Structure of the Yellow-Green Fluorescent Peptide Produced by Iron-deficient Azotobacter vinelandii Strain O. Tetrahedron 28 5359... 

Salah-el-Din ALM, Kyslik P, Stephan D, Abdallah MA (1997) Bacterial Iron Transport Structure Elucidation by FAB-MS and by 2D NMR ( H, C, N) of Pyoverdin G4R, a Peptidic Siderophore Produced by a Nitrogen-Fixing Strain of Pseudomonas putida. Tetrahedron 53 12539... 

Active Site Structure of Rubredoxin There are several non-heme iron-sulphur proteins that are involved in electron transfer. They contain distinct iron-sulphur clusters composed of iron atoms, sulphydryl groups from cysteine residues and inorganic or labile sulphur atoms or sulphide ions. The labile sulphur is readily removed by washing with acid. The cysteine moieties are incorporated within the protein chain and are thus not labile. The simplest type of cluster is bacteria rubredoxin, (Cys-S)4 Fe (often abbreviated FelSO where S stands for inorganic sulphur), and contains only non labile sulphur. It is a bacterial protein of uncertain function with a molecular weight of 6000. The single iron atom is at the centre of a tetrahedron of four cysteine ligands (Fig.). 

Paiaro, G., R. Palumbo, A.Musco, and M. Panunzi The resolution of the fumaric acid-iron-tetracarbonyl complex. Tetrahedron Letters [London] 1965, 1067. 

Trifan, D. S., and R. Bacskai The role of iron in carbonium ion reactions of ferrocene derivatives. Tetrahedron Letters [London] 1960/13, 1. 

Without mctai-metnl bonds, ihese complexes would have 17, 16. and IS electrons per metal atom, respectively. The deficiencies are compensated bv one, two. and three M—M bonds per metal.. Structures for the two iron complexes arc shown in Fig. 15.7. In the tctracobalt complex, the four metal atoms are arranged in the form of a tetrahedron with the Co atoms occupying the corners and the six metal-metal bonds forming the edges. Larger clusters such as Co fCO), are also known, but the 18-electron rule breaks down for complexes with more than four metal atoms. In these species, electron delocalization is extensive, and other models (described in Chapter 16) are of greater value.11... 

In the case of a commercial NaY zeolite ((Na2O)i.04 X A1203 X (Si02)5.2, 0.07 wt % iron from VEB CK Bitterfeld-Wolfen) a surprisingly strong effect was observed with small platinum content only 1 wt % platinum was introduced by exchange with the complex [Pt(NH3)4]2+. In the case of a statistical distribution of this platinum over the zeolite, the probability for one Fe3+ in the zeolite lattice (Fe04 tetrahedron) to be... 

G. H. Veeneman, S. H. van Leeuwen, and J. H. van Boom, lodonium ion promoter reactions at the anomeric centre. II. An efficient thioglycoside mediated approach toward the formation of 1,2-irons linked glycosides and glycosidic esters, Tetrahedron Lett. 3/ 1331 (1990). 

Another group of related electron carriers, the high-potential iron proteins (HIPIP) contain four labile sulfur and four iron atoms per peptide chain 261-266 X-ray studies showed that the 86-residue polypeptide chain of the HIPIP of Chromatium is wrapped around a single iron-sulfur cluster which contains the side chains of four cysteine residues plus the four iron and four sulfur atoms (Fig. 16-15D)261 This kind of cluster is referred to as [4Fe-4S], or as Fe4S4. Each cysteine sulfur is attached to one atom of Fe, with the four iron atoms forming an irregular tetrahedron with an Fe-Fe... 

Rubredoxins. The simplest of the Fe-S proteins are the rubredoxins. These proteins contain iron but no labile sulfur. The rubredoxin of Clostridium pastcur-ianum is a 54-residue peptide containing four cysteines whose side chains form a distorted tetrahedron about a single iron atom (Fig. 16-16A).274 Not shown for any... 

In both [Fe4X4(N0)4](X = S or Se) and [Fe4S2(NO)4(NCMe3)2] the total valence electron count is 60. This is the number characteristic of tetrahedral tetranuclear metal clusters, such as [Ir4(CO)12], in the Wade and Mingos skeletal-electron counting schemes (76, 77) and, furthermore, each iron atom in these clusters obeys the 18-electron rule, provided that it forms single Fe-Fe bonds to each of the other iron atoms in the tetrahedron. 

SPHALERITE BLENDE. Also known as zinc blende, this mineral is zinc sulfide, tZn, Fc)S, practically always containing some iron, crystallizing in the isometric system frequently as tetrahedrons, sometimes as cubes or dodecahedrons, but usually massive with easy cleavage, which is dodecahedral. It is a brittle mineral with a conchoidal fracture hardness, 2.5-4 specific gravity, 3.9-4.1 luster, adamantine to resinous, commonly the latter. It is usually some shade of yellow brown or brownish-black, less often red, green, whitish, or colorless streak, yellowish or brownish, sometimes white transparent to translucent. Certain varieties... 

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